I've got a FlightAware Blue USB plugged into my Windows 10 machine and can see "limited info" using RTL1090 but when going to
Virtual Radar Server, I am totally lost in the absence of a good tutorial suitable for newbies.

Preset Configurations, why are 2 receivers required to be inputted?
What address do you use, the Machine Address 192. 168.xxx.xxx ?
or 192.168.xxx.xxx:1234?

How do you determine the PORT NUMBER?
Where do you see an assigned or how do you assign a PORT NUMBER?

FIREWALL.
I gain the impression that your cable modem stops inbound traffic?
I can choose
Allow individual Application(s)
then it wants me to "choose" from an Applications list that does not include Virtual Radar Server.
It has Flight Simulator 2000, 2002, 2004 Flight Simulator X or
an option for "ADD A NEW USER-DEFINED APPLICATION

I added Application Profile Name Virtual Radar Server
Protocol TCP OR UDP (TCP being the default)
PORT ( OR RANGE) FROM: TO:
I opened up 30001 to 3003 Port 80

Only apparent option was a Virtual Private Network.

Fire Virtual Radar Server back up and while able to see a google map centered on my QTH
I am unable to see any aircraft. Fire rtl1090.beta3.exe
back up and am able to see aircraft locally, no map , but list of airports and navaids on "Scope".

I would like to make my data available anyone and to set up other local
receivers to provide MLAT.

I think you might be the guy who emailed me over Christmas? I had a series of emails from someone with a FlightAware USB receiver who might be confusing VRS with something else, which might be the case here as well. VRS does not ask for two receivers before it'll work, you can just enter one.

Presumably you have some software already decoding the messages coming off the FlightAware stick - if so, and if that software lets you send that feed across your network to another machine, then the port number you enter for the receiver is the port that the other bit of software is listening to for requests for feeds.

Firewall questions about cable modems - I can't help much there. Every manufacturer of modem, router and firewall will be set up differently. If you have a popular make of cable modem then you could try googling for "<make and model of cable modem> open port". However, if you're asking about receiver port numbers then I'm not sure that you've managed to get VRS running locally... I would cross that bridge first, worry about putting the site onto the Internet later.